How to add raised text to an imported STL file for 3D printing
When importing STL change Scale to 0.001 to get proper size ... right now your Cattle has a dimension 73 x 99 m.

Now add a Text object ...

... that becomes big by default so scale S it down

WIth Tab switch to edit mode type your text. Add Solidify modifier to get thickness of letters.

Search for Convert to Mesh, hide this object in Outliner Editor. Select Cattle object add Boolean modifier kind Union and as Object select your Text object.

Before export use again Convert to Mesh (or apply modifier under arrow down icon) to make manifold object. ready for 3D printer.

I would suggest to you check some tutorial for beginners to get friendly with blenders UI first.